Analysis of vertical sound image control with parametric loudspeakers

Abstract

A parametric loudspeaker is known as a super directional loudspeaker by using nonlinear interaction between high power ultrasounds in air. The parametric loudspeaker is one of the prominent applications of nonlinear acoustics. So far, we had conducted the listening test that the parametric loudspeaker reproduced left and right signals with binaural information. The characteristics of the sound localization with the upper and lower parametric loudspeakers in the vertical direction were investigated by the results of listening tests. The vertical direction of sound localization was able to be controlled when the acoustical axis was set to the right ear. The results were similar as in using ordinary loudspeakers. It was found that the left-right sound localization could be realized only with the upper and lower parametric loudspeakers. By setting the parametric loudspeaker the right ear, that is by setting it only 3 degrees rightward, the direction of sound localization moved about 10 degrees rightward. In order to make clear the obtained new finding, the effect of the acoustic axis of the parametric loudspeaker to the direction of left-right sound localization was analyzed in details. The ILD (Interaural Level Difference) were calculated by introducing a simple geometrical model of a listener head.